(Aluminum sulfate, Aluminum acetate)
Of the mineral mordants, alum is the most used and has been known as a mordant from early times in many parts of the world. For most colors a certain proportion of cream of tartar is often added to the alum bath as it helps to brighten the ultimate color. The usual amount of alum is 10 - 25% the weight of the wool or fiber. As a rule, less mordant, as little as 10% of the weight of wool, is needed for lighter colors than for dark. Excess of alum is apt to make the wool sticky. The usual length of time for boiling is about an hour. Some dyers give as much as 2-1/2 hours. There is also a cold method whereby the wool is added to a cold alum bath and left for one to two weeks.
Example of mordanting with alum—1/4 lb. of Alum and 1 oz. cream of tartar for every pound of wool (metric: 125 gm alum and 30 gm cream of tartar for every 500 gm of wool). This is dissolved and when the water is warm the wool is entered. Raise to boiling point and boil for one hour. The bath is then taken off the heat and allowed to cool over night. The wool is then very gently wrung out (not washed) and put away in a linen bag in a cool place for 4 or 5 days, when it is ready for dyeing, after being thoroughly rinsed.
Another form of alum is Alum Acetate which is more specific and beneficial for dyeing cellulose fibers like cotton, linen and hemp. These fibers should first be mordanted with some form of tannic acid or high tannin plant mordant to help bind alum. The same is true for alum acetate although I have used it without the first step with good results. Alum acetate is available from natural dye suppliers but unlike regular alum, can be a bit difficult to find from chemical supply companies. It is also significantly more expensive but worth the cost for the superior results with cellulose.
(Ferrous Sulphate, copperas, green vitriol)
Iron is one of the oldest mineral mordants known and is largely used in wool and cotton dyeing. It is almost as important as alum. The temperature of the mordanting bath must be raised very gradually to boiling point or the wool will dye unevenly. A general method of dealing with iron is to boil the wool first in a decoction of the coloring matter and then add the mordant to the same bath in a proportion of 5 to 8 per cent of the weight of the wool, and continue boiling for half an hour or so longer. With some dyes a separate bath is needed, such as with Camwood or Catechu. Great care is needed in using iron, as, unless it is thoroughly dissolved and mixed with the water before the wool is entered, it is apt to stain the wool. It also hardens wool if used in excess or if boiled too long. A separate bath should always be kept for natural dyes or mordants containing iron. The least trace of it will dull colours and it will spoil the brilliancy of reds, yellows and oranges.
Iron is mostly used for the fixing of wool colors (Fustic, etc.) to produce brown shades; the wool being boiled first in a decoction of the natural dye for about 1 hour, and then for 1/2 an hour with the addition of 5 to 8 per cent of iron. If used for darkening colors, iron is added to the bath after the dyeing, and the boiling continued for 15 to 20 mins.
(Stannous chloride, tin crystals, tin salts, muriate of tin.)
Tin is not so useful as a mineral mordant in itself, but as a modifying agent with other mordants. It must always be used with great care, as it tends to harden the wool, making it harsh and brittle. Its general effect is to give brighter, clearer and faster colors than the other mordants. When used as a mordant before dyeing, the wool is entered into the cold mordant bath, containing 4 per cent of stannous chloride and 2 per cent oxalic acid; the temperature is gradually raised to boiling, and kept at this temperature for 1 hour. It is sometimes added to the natural dye bath towards the end of dyeing, to intensify and brighten the color. It is also used with cochineal for scarlet on wool in the one bath method.
(Potassium dichromate. Bichromate of Potash.)
Chrome is a modern mineral mordant. It is excellent for wool and is easy to use and very effective in its action. Its great advantage is that it leaves the wool soft to the touch, whereas the other mordants are apt to harden the wool. The disadvantage is that chrome is considered an environmentally toxic mordant and must be disposed of properly. For this reason, many natural dyers choose not to use chrome.
The wool should be boiled for 1 to 1-1/2 hours with chrome in the proportion of 2 to 4 per cent of the wool. It is then washed well and immediately dyed. Wool mordanted with chrome should not be exposed to light, but should be kept well covered with the liquid while being mordanted, or it is liable to dye unevenly. An excess of chrome impairs the color; 3 per cent of chrome is a recommended quantity to use for ordinary dyeing. It should be dissolved in the bath while the water is heating. The wool is entered and the bath, gradually raised to the boiling point, and boiled for 3/4 of an hour.
(Copper Sulphate, Verdigris, Blue Vitriol, Blue Copperas, Bluestone)
Copper is rarely used as a mineral mordant. It is usually applied as a saddening agent, that is, the wool is dyed first, and the mordant applied afterwards to fix the color. With cream of tartar it is used sometimes as an ordinary mordant before dyeing, but the colors so produced have no advantage over colors mordanted by easier methods.
Adapted from: VEGETABLE DYES: Being a Book of Recipes and Other Information Useful to the Dyer by ETHEL M. MAIRET
*If you are considering using chrome or potassium dichromate (bichromate of potash) as a mineral mordant for your natural dyes, read this article first - WHY WE DON'T USE CHROME ANYMORE! by Darvin DeShazer, USA (The International Mushroom Dye Institute)
Go from Mineral Mordants to Herbal Mordants
Blue Castle Fiber Arts is a small on-line fiber arts business and importer of natural dyes from India. We are located on the beautiful shores of Lake Ontario in Hamilton, Ontario, Canada.
This website focuses on our easy-to-use natural dyes and you will find plenty of information about them and how to use them. You can also visit our supplier's website here: Sam Vegetable Colours.